1. Field of the Invention
The invention relates to an image forming apparatus, which can optimize the rising sequence of a fan and shorten the time from the start of a copy job to the delivery of the first sheet out of the apparatus.
2. Description of Related Art
An example of the image forming apparatus according to the prior art will hereinafter be described with reference to FIGS. 6 and 7 of the accompanying drawings.
FIG. 6 is a typical cross-sectional view of a photosensitive member, a transferring device, a stripping device, a transport device and a fixing device in an image forming portion contained in the image forming apparatus (not shown).
FIG. 7 simply shows the relation between the time from the standby state through the copying operation to the stop of the copying operation of the image forming apparatus and the operation sequence of a fan.
As shown in FIG. 6, a sheet P transported to registration rollers 501 as sheet supplying means by feeding and transporting means (not shown) comes into between a photosensitive drum 502 which is a photosensitive member bearing thereon a toner image formed by electrophotography and being rotated and transferring means 503 and stripping means 504 disposed in proximity to and opposed relationship with the photosensitive drum 502.
In a transferring area, the sheet P begins to contact with the photosensitive drum 502 which is an image bearing member, passes through the transferring area and arrives at the corona discharge area of the stripping means 504, whereupon the sheet P which has so far been in contact with the photosensitive drum 502 is stripped from the photosensitive drum 502.
The sheet P thus stripped is completely stripped from the photosensitive drum 502 by suction means 505 playing the auxiliary role of the stripping means 504, and is sent to transporting means 506 along a guide 507 provided on the sheet passing surface of the stripping means 504. The suction means 505 is comprised of a duct 508 and a stripping fan 509.
Further, the transporting means 506 is comprised of a driving runner 510, a driven runner 511 and a transport belt 513 looped around and driven by the driving runner 510 and the driven runner 511. The transported sheet P is transported to fixing means 514 by the transport belt 513.
Here, the stripping fan 509 assumes the starting sequence as shown in FIG. 7. In a graph as shown in FIG. 7, a section up to time T1 of a line designated by xe2x80x9caxe2x80x9d represents the standby state of the image forming apparatus. In the standby state, a user performs a series of operations in preparation for the copying operation, and when he depresses a copy start button at T1, the stripping fan 509 is started. The stripping fan 509 rises to a use, rotating speed at T1-T3. T2 and T2xe2x80x2 indicate the time when the leading edge of the sheet P arrives at the registration rollers 501.
If the leading edge of the sheet P has already arrived at the registration rollers 501 at T2 (T2 less than T3), the sheet P stands by at the position of the registration rollers 501 until T3 when the stripping fan 509 rises. Or if the leading edge of the sheet P has arrived at the registration rollers 501 at T2xe2x80x2 (T2xe2x80x2 greater than T3) whereat the stripping fan 509 is already in its rising state, the sheet P does not stand by at the registration rollers 501 but shift is made to the image forming operation.
Thereafter, the image forming operation is started and at T4, the last sheet P is delivered out of the image forming apparatus, whereupon the stripping fan 509 performs the stopping operation.
Also, if as previously described, in the line designated by xe2x80x9caxe2x80x9d in the graph, the leading edge of the sheet P arrives at the registration rollers 501 at T2, as a measure for shortening the time for which the sheet P stands by at the position of the registration rollers 501, use has been made of a sequence as shown by a line designated by xe2x80x9cbxe2x80x9d in the graph for pre-starting the stripping fan 509 in the standby state.
In recent years, as seen in an image forming apparatus such as a copying machine or a printer for forming an image which is provided with a post-processing apparatus having the functions of sorting, stapling, punching and binding sheets on which images have been formed, the complication of the apparatus system has been advanced while on the other hand, the higher speed of the apparatus has also been advanced to improve productivity. Further, with the advance of the higher speed of the apparatus on the one hand, the trend for energy saving has become popular as the consideration for environmental problems. So, the above-described prior art has suffered from such problems as will be shown below.
In the prior-art image forming apparatuses of low and medium speeds, a method of corona-discharging to a sheet has been popular as a method of stripping a sheet from a photosensitive member. In recent years, however, the higher speed of the image forming apparatuses have been advanced to improve productivity and it has become difficult to strip a sheet from the photosensitive member by the aforedescribed stripping method alone. For example, as the image forming apparatus becomes higher in speed, the rotating speed of the photosensitive member increases and therefore, sufficient discharge is not done to the sheet and bad stripping may result and jam may sometimes be caused.
So, a solution to these problems has been attempted by a countermeasure such as strengthening the discharge current or sucking the sheet by a fan through a duct in the stripping portion. Also, in order that the sheet stripped from the photosensitive member may be standby transported to the fixing means even if the higher speed is advanced, use has often been made of a fan in the transporting means to suck the sheet by the fan through a duct to thereby suck the sheet onto the transporting means as well as to satisfy stable transportability.
However, when the higher speed is further advanced, suction means greater in suction force becomes necessary in order to improve the aforementioned separability and transportability. Consequently, the fan necessarily becomes bulky and this has led to such a problem as will be described below.
A bulky fan, as compared with the fan heretofore used, becomes long in its rising time and therefore, if for example, the fan is started from a point of time at which the user has operated a copy button to thereby start a copy job, a certain extent of time is required until the rotation of the fan becomes stable and thus, even a sheet started to be transported stops at a predetermined position for the time until the rotation of the fan becomes stable. This leads to the problem that the time until the first sheet after the start of the copy job is delivered out of the apparatus becomes long, and this is against the aforedescribed improvement in the productivity of the image forming apparatus.
Therefore, in the prior art, the shortening of the rising time has been contrived by operating the fan at a half of the ordinary use rotating speed or keeping the fan at the ordinary use rotating speed in the standby state of the image forming apparatus. However, depending on the installation environment (temperature and humidity) of the image forming apparatus or the type of paper great in rigidity such as thick paper good in separability, there is a case where the rotating speed of the fan is excessive. In such case, the fan is operated even during a time when the suction of a sheet is not required and thus, consumes extra electric power, and this is against the above-described trend for energy saving.
The present invention has been made in order to solve the above-noted problems peculiar to the prior art and the object thereof is to provide an image forming apparatus in which the rising sequence of a fan made bulkier with the higher speed of the image forming apparatus is reconsidered and the time from the start of a copy job until the first sheet is delivered out of the apparatus is shortened to thereby make high productivity possible and as the consideration for environmental problems, the consumption of extra electric power in the standby state of the image forming apparatus is suppressed.
In order to achieve the above object, an image forming apparatus according to the present invention comprises:
sheet supplying means for supplying a sheet to a photosensitive member;
transferring means for transferring an image from the photosensitive member to the sheet;
stripping means provided downstream of the transferring means in the transport direction of the sheet for stripping the sheet from the photosensitive member;
transporting means for transporting the stripped sheet to fixing means;
a duct having an opening portion on the stripping means side thereof;
one or more fans provided in the other opening portion of the duct to suck a side opposite to a side of the sheet on which the image is formed; and
operation signal detecting means for detecting electrical signals by a user""s predetermined operation in preparation for the start of a copy job, and
when the operation signal detecting means detects at least one of the electrical signals by the predetermined operation, at least one of the fans is started in synchronism with the detection signal thereof.
Also, an image forming apparatus according to the present invention comprises:
sheet supplying means for supplying a sheet to a photosensitive member;
transferring means for transferring an image from the photosensitive member to the sheet;
stripping means provided downstream of the transferring means in the transport direction of the sheet for stripping the sheet from the photosensitive member;
transporting means for transporting the stripped sheet to fixing means;
a duct having an opening portion on the transporting means side thereof;
one or more fans provided in the other opening portion of the duct to suck a side opposite to a side of the sheet on which the image is formed; and
operation signal detecting means for detecting electrical signals by a user""s predetermined operation in preparation for the start of a copy job, and
when the operation signal detecting means detects at least one of the electrical signals by the predetermined operation, at least one of the fans is started in synchronism with the detection signal thereof.
It is preferable that after the termination of the operation of the image forming apparatus, at least one of the fans be stopped after it is operated for a predetermined time while maintaining a predetermined rotating speed.
It is preferable that when the operation signal detecting means detects at least one of the electrical signals by the predetermined operation, at least one of the fans be started in synchronism with the detection signal thereof, and when the image forming apparatus does not detect an image forming signal for a predetermined time, the fans be stopped.
The image forming apparatus has environment detecting means for detecting environment, and it is preferable that when the operation signal detecting means detects at least one of the electrical signals by the predetermined operation and the environment detecting means detects that the apparatus is in predetermined environment, the fans maintain their stopped state, and the fans be started in synchronism with the signal of the user""s copy job starting operation.
The image forming apparatus has environment detecting means for detecting environment, and it is preferable that the rotating speed of the fans be fluctuated in conformity with the environment detected by the environment detecting means.
Also, an image forming apparatus according to the present invention comprises:
sheet supplying means for supplying a sheet to a photosensitive member;
transferring means for transferring an image from the photosensitive member to the sheet;
stripping means provided downstream of the transferring means in the transport direction of the sheet for stripping the sheet from the photosensitive member;
transporting means for transporting the stripped sheet to fixing means;
a duct having an opening portion on the stripping means side thereof;
one or more fans provided in the other opening portion of the duct to suck a side opposite to a side of the sheet on which the image is formed; and
environment detecting means for detecting environment, and
when the environment detecting means detects that the apparatus is in a predetermined environment, the rotation of the fans is stopped or the rotating speed of the fans is fluctuated.
Also, an image forming apparatus according to the present invention comprises:
sheet supplying means for supplying a sheet to a photosensitive member;
transferring means for transferring an image from the photosensitive member to the sheet;
stripping means provided downstream of the transferring means in the transport direction of the sheet for stripping the sheet from the photosensitive member;
transporting means for transporting the stripped sheet to fixing means;
a duct having an opening portion on the stripping means side thereof;
one or more fans provided in the other opening portion of the duct to suck a side opposite to a side of the sheet on which the image is formed; and
type detecting means for detecting the type of the sheet, and
when the type detecting means detects that the sheet is a predetermined type of paper, the rotation of the fans is stopped or the rotating speed of the fans is fluctuated in conformity with the type of paper.
As described above, the fans rise while the user is performing a predetermined operation in preparation for a copy job and therefore, it becomes possible to shorten the time from after the start of the copy job until the first sheet is delivered out of the image forming apparatus, and high productivity can be secured.
Further, the fans are stopped in the standby state of the image forming apparatus and therefore, it becomes possible to suppress the consumption of extra electric power, and by changing the rotating speed of the fans to a necessary rotating speed in conformity with the installation environment of the image forming apparatus or the type of the sheet, it becomes possible to suppress the consumption of extra electric power, and the purpose of the consideration for environmental problems can be achieved.
As described above, the present invention starts the fans when the electrical signal by the predetermined operation before the start of the copy job, to thereby shorten the time from after the start of the copy job until the first sheet is delivered out of the apparatus, whereby high productivity is made possible and it becomes possible to suppress the consumption of extra electric power in the standby state of the image forming apparatus.